| 1. |
- Schiebe, Christian
(författare)
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Attraction and resistance in the Picea abies – Ips typographus system : host choice in the Eurasian spruce bark beetle
- 2012
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Decades of research have gathered detailed knowledge about the Eurasian spruce bark beetle (Ips typographus L.) and its interaction with its host tree Norway spruce (Picea abies (L.) H Karst). The strong pheromone attraction enabling this beetle to kill healthy host trees is a well known process, and pheromones are widely used to trap beetles in forest pest management. Yet, host finding and final host choice by the first attacking pioneer beetles is only vaguely understood. The aim of this thesis was to identify olfactory cues for host choice from habitat to final colonisation. The importance of non-host volatiles (NHV) and old-host volatiles (OHV) for habitat finding, indicating unsuitable habitats, was confirmed in a large scale field experiment at forest edges in Slovakia and Sweden. A blend of NHV/OHV dispensers created an artificial semiochemical diversity, and reduced attacks in treated versus untreated plots. An active inhibitory range of ≈15 m was determined for the protection. A detailed study of host bark chemistry in relation to natural bark beetle attacks showed the importance of induced host defence capacity for resistance in P. abies against I. typographus attacks. The only individual host compound that seemed to influence host choice in this study was 1,8-cineole. Volatiles that were collected from bark of felled and standing healthy trees were tested on I. typographus antennae by using combined gas chromatography-electroantennographic detection. The electrophysiological studies also including single sensillum recording technique revealed eight novel ligands of host compounds, of which six are oxygenated, eliciting strong responses in olfactory sensory neurons. Proportional increase of oxygenated host compounds in host chemistry were shown to be related to induced defence and decay of host bark, and are proposed as semiochemicals for host evaluation by I. typographus. Quantification of host volatiles released by felled, healthy, and naturally attacked standing trees indicate that the onset of beetle attack correlated with high amounts of released host volatiles. Field trapping experiments and laboratory no-choice feeding assays with a subset of the oxygenated compounds confirmed the inhibiting activity of 1,8-cineole, and indicated both negative and positive effects on pheromone attraction and feeding by other antennally active compounds.
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| 2. |
- Schiebe, Christian
(författare)
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Host choice mechanisms in tree killing bark beetles : an overview of joint knowledge and a suggested model of host choice mechanisms in the European spruce bark beetle
- 2011
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- Bark beetles with the capacity to kill and colonize living trees are main pests of coniferous forests around the world. The European spruce bark beetle, Ips typographus, belongs to a group of bark beetles possessing facultative attack patterns. For long periods I. typographus is living in low populations only on seriously weakened hosts. However, following disturbances like storms or drought periods, the amount of suitable breading material increases dramatically and the population size of beetles may rise within a short time to epidemic levels. In the epidemic phase I. typographus behaves aggressively, attacking healthy trees and destroying large areas of Norway spruce forest. Bark beetles with this pattern of behaviour are exploiting a different ecological niche than during the endemic, low population phase: in broken or seriously weakened hosts they exploit a relatively poor source of nutrients without dealing with host defences. Instead they have to deal with a higher degree of interspecific competition. On the other hand, a living host provides breeding material, which is rich in nutrients and relatively free from interspecific competition, but there beetles have to fight the defence responses of the host tree. Host defences can be overcome by mass attack of thousands of beetles on the same tree, which is coordinated by aggregation pheromones. The trade-off between evaluating host quality and risk rating host defences is a great challenge for the pioneering beetles, that initiate an attack before any pheromone plumes exist. The host choice mechanism can be divided in several distinct steps: 1. habitat location during flight 2. host location during flight 3. host evaluation after landing, involving detection of host suitability and spacing between species and individuals to avoid inter- or intraspecific competition. 4. risk rating host defences after entrance into host phloem. The question whether the beetles’ attack behaviour is ruled by pheromone attraction alone or is guided by markers for host suitability has been an issue of debate for decades. The peripheral nervous system of bark beetles possesses olfactory receptor neurons for both pheromones, host volatiles and non-host volatiles. Several studies support the theory that non-host volatiles cues play an important role in habitat location, while host volatiles are involved in host finding and host acceptance, either alone or through modulating pheromone attraction. Host defence responses consist of physical barriers and chemical compounds that may be detrimental to invaders. Conifers maintain a certain level of preformed (constitutive) defence that can be enhanced during and after the attacks, e.g. by the increased production of defensive metabolites and development of defensive structures. The different metabolites involved in a trees defence responses may be important markers for beetles to evaluate the trees’ defensive ability, and guide them in their decision to enter a host. Because the population density is an important factor influencing the beetles’ success in overwhelming a trees defence, it has been hypothesized that it also will modulate beetles behaviour, either directly or through its influence on the beetles’ quality. This introductory paper is written to obtain an overview over the literature dealing with different aspects of host choice in bark beetle species exhibiting so called aggressive host colonisation behaviour. Different hypotheses and aspects of importance for the host choice behaviour are discussed. Finally, I propose a host choice model for the European spruce bark beetle Ips typographus
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| 3. |
- Schiebe, Christian, et al.
(författare)
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Inducibility of chemical defenses in Norway spruce bark is correlated with unsuccessful mass attacks by the spruce bark beetle
- 2012
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Ingår i: Oecologia. - : Springer Science and Business Media LLC. - 0029-8549 .- 1432-1939. ; 170:1, s. 183-198
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Tidskriftsartikel (refereegranskat)abstract
- Secondary attraction to aggregation pheromones plays a central role in the host colonization behavior of the European spruce bark beetle Ips typographus. However, it is largely unknown how the beetles pioneering an attack locate suitable host trees, and eventually accept or reject them. To find possible biomarkers for host choice by I. typographus, we analyzed the chemistry of 58 Norway spruce (Picea abies) trees that were subsequently either (1) successfully attacked and killed, (2) unsuccessfully attacked, or (3) left unattacked. The trees were sampled before the main beetle flight in a natural Norway spruce-dominated forest. No pheromones were used to attract beetles to the experimental trees. To test the trees' defense potential, each tree was treated in a local area with the defense hormone methyl jasmonate (MeJ), and treated and untreated bark were analyzed for 66 different compounds, including terpenes, phenolics and alkaloids. The chemistry of MeJ-treated bark correlated strongly with the success of I. typographus attack, revealing major chemical differences between killed trees and unsuccessfully attacked trees. Surviving trees produced significantly higher amounts of most of the 39 analyzed mono-, sesqui-, and diterpenes and of 4 of 20 phenolics. Alkaloids showed no clear pattern. Differences in untreated bark were less pronounced, where only 1,8-cineole and (-)-limonene were significantly higher in unsuccessfully attacked trees. Our results show that the potential of individual P. abies trees for inducing defense compounds upon I. typographus attack may partly determine tree resistance to this bark beetle by inhibiting its mass attack.
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| 4. |
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| 5. |
- Schiebe, Christian, et al.
(författare)
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Semiochemical diversity diverts bark beetle attacks from Norway spruce edges
- 2011
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Ingår i: Journal of applied entomology. - : WILEY. - 0931-2048 .- 1439-0418. ; 135:10, s. 726-737
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Tidskriftsartikel (refereegranskat)abstract
- The semiochemical diversity hypothesis (SDH) states that interference with host-selection from non-host volatiles (NHV) is an important mechanism for associational resistance. Inhibition of bark beetle attraction to point sources by non-host volatiles (NHV) is well established and might be a signal serving in host-selection also at the habitat scale. In forests dominated by Norway spruce in middle and northern Europe (N Slovakia 2006 & 2007, SE Sweden 2007), we applied a blend of NHV and verbenone, released from dispensers fixed at 2 and 6 m height at forest edges with high Ips typographus populations. In Slovakia, three different doses (0.2–0.7 dispensers/m forest edge) were tested in 20-tree zones of spruce stand edges. The Swedish experiments used only the middle dose. In Slovakia, there was high tree mortality but dispensers with the anti-attractants reduced killed trees in a dose-dependent manner. The reduction in tree killing ranged from 35 to 76% compared to untreated zones. Regression analysis of relative tree kill on log dispenser density was highly significant (R2ADJ= 0.34, corresponding effect size d≈ 0.98). In Sweden, with lower beetle populations, most attacks (99%) were found outside the experimental areas, with high attack rates (15 trees/ha) in a range of 15–30 m from treated groups, indicating an active inhibitory radius exceeding the previous estimates. The SDH as a functional aspect of biodiversity was tested by converting spruce monocultures into an artificial semiochemically mixed forests. The use of NHV provides the only non-insecticidal method of direct protection of conifer forests. The demonstrated principle of protection is still too expensive for area-wide use, but viable for high-value areas (nature reserves). Further development of push–pull strategies or area-wide applications may prove more cost efficient. In the long-term, the only sustainable approach is a forest landscape of mixed habitats.
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| 6. |
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| 7. |
- Schiebe, Christian, et al.
(författare)
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Styrene, (+)-trans-(1R,4S,5S)-4-Thujanol and Oxygenated Monoterpenes Related to Host Stress Elicit Strong Electrophysiological Responses in the Bark Beetle Ips typographus
- 2019
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Ingår i: Journal of Chemical Ecology. - : Springer. - 0098-0331 .- 1573-1561. ; 45:5-6, s. 474-489
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Tidskriftsartikel (refereegranskat)abstract
- Bark beetles kill apparently vigorous conifers during epidemics by means of pheromone-mediated aggregation. During non-endemic conditions the beetles are limited to use trees with poor defense, like wind-thrown. To find olfactory cues that help beetles to distinguish between trees with strong or weak defense, we collected volatiles from the bark surface of healthy felled or standing Picea abies trees. Furthermore, living trees were treated with methyl jasmonate in order to induce defense responses. Volatiles were analyzed by combined gas chromatography and electroantennographic detection (GC-EAD) on Ips typographus antennae. Compounds eliciting antennal responses were characterized by single sensillum recording for identification of specific olfactory sensory neurons (OSN). Release of monoterpene hydrocarbons decreased, while oxygenated compounds increased, from spring to early summer in felled trees. In both beetle sexes particular strong EAD activity was elicited by trace amounts of terpene alcohols and ketones. 4-Thujanol gave a very strong response and the absolute configuration of the tested natural product was assigned to be (+)-trans-(1R,4S,5S)-thujanol by stereoselective synthesis and enantioselective gas chromatography. One type of OSN responded to all ketones and five other OSN were characterized by the type of compounds that elicited responses. Three new OSN classes were found. Of the eight EAD-active compounds found in methyl jasmonate-treated bark, the known anti-attractant 1,8-cineole was the one most strongly induced. Our data support the hypothesis that highly active oxygenated host volatiles could serve as positive or negative cues for host selection in I. typographus and in other bark beetles.
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| 8. |
- Schlyter, Fredrik, et al.
(författare)
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Björkdoft mot granbarkborrar
- 2009
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Ingår i: Skogseko. - 0346-0495. ; , s. 12-13
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Tidskriftsartikel (populärvet., debatt m.m.)abstract
- Granbarkborre och doftdiversitet Utan tvivel skulle hotet från granbarkborren minska om södra Sverige till större del bestod av bland- och lövskogar. Så visar Jactel och Brockerhoff (2007) i en metaanalys av 119 artiklar att blandskogar oftast uppvisar färre insektsskador – särskilt när det gäller specialister som granbarkborren. Det ju rätt uppenbart att specialiserade skadeinsekter har svårare att föröka sig när värdväxten blir mindre talrik. Men en stor roll spelar också doftdiversiteten: svårigheten att hitta värdväxten för en luktstyrd insekt, när lukter från olika växter blandas. Många människor känner till att insekters egna artspecfika signalsubstanser, feromoner, är oerhört kraftfulla signaler, som kan användas för att t.ex. lura en art som är skadedjur i mängder in i fällor. Att denna signal fungerar i praktiken vet alla som satt upp en barkborrefälla efter Gudrun! Att insekter dras till dofter från sina värdväxter är ju också känt sen länge, men att de också reagerar kraftigt på vissa dofter från icke-värdväxter är bara känt sedan drygt 15 år. Barkborrar på barrträd både i Europa och Nordamerika är bland de bäst studerade insekterna vad gäller doftdiverstitet. Anledningen är ju ganska uppenbar: sådana dofter skulle kunna tänkas användas för att ’lura’ t.ex. ett barrträdsdjur att det befinner sig i en lövskog och bör söka sig bort från området. Även om alla aktörer inom skogs-Sverige vore överens om att ändra inriktningen bort från gran omedelbart, hade vi en verklighet med kraftig grandominans att hantera under lång tid framöver. Här skulle ”konstgjorda blandskogar” med icke-värdväxtdofter kunna erbjuda en alternativ lösning i utsatta skogspartier, särskilt när ett varmare klimat ökar hotet från barkborrarna
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| 9. |
- Unelius, C. Rikard, et al.
(författare)
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Non-Host Volatile Blend Optimization for Forest Protection against the European Spruce Bark Beetle, Ips typographus
- 2014
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Ingår i: PLOS ONE. - : Public Library of Science (PLoS). - 1932-6203. ; 9:1
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Tidskriftsartikel (refereegranskat)abstract
- Conifer feeding bark beetles (Coleoptera, Curculionidae, Scolytinae) pose a serious economic threat to forest production. Volatiles released by non-host angiosperm plants (so called non-host volatiles, NHV) have been shown to reduce the risk of attack by many bark beetle species, including the European spruce bark beetle, Ips typographus. However, the most active blend for I. typographus, containing three green leaf volatiles (GLVs) in addition to the key compounds trans-conophthorin (tC) and verbenone, has been considered too expensive for use in large-scale management. To lower the cost and improve the applicability of NHV, we aim to simplify the blend without compromising its anti-attractant potency. Since the key compound tC is expensive in pure form, we also tested a crude version: technical grade trans-conophthorin (T-tC). In another attempt to find a more cost effective substitute for tC, we evaluated a more readily synthesized analog: dehydroconophthorin (DHC). Our results showed that 1-hexanol alone could replace the three-component GLV blend containing 1-hexanol, (3Z)-hexen-1-ol, and (2E)-hexen-1-ol. Furthermore, the release rate of tC could be reduced from 5 mg/day to 0.5 mg/day in a blend with 1-hexanol and (-)-verbenone without compromising the anti-attractant activity. We further show that T-tC was comparable with tC, whereas DHC was a less effective anti-attractant. DHC also elicited weaker physiological responses in the tC-responding olfactory receptor neuron class, providing a likely mechanistic explanation for its weaker anti-attractive effect. Our results suggest a blend consisting of (-)-verbenone, 1-hexanol and technical trans-conophthorin as a cost-efficient anti-attractant for forest protection against I. typographus.
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| 10. |
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